1. Field of the Invention
This invention relates to cyclic carbonate compounds useful as a dissolution inhibitor for chemically amplified positive photoresists, a process for producing said compounds, and a positive photoresist composition using said compounds.
2. Related Art
Due to the recent improvement in the degree of integration of integrated circuits (64 or 256 MDRAM), it is desired that today's photoresists have an ability to form sub-micron patterns. Thus, development of a positive type photoresist suitable for use in the far ultraviolet lithography such as those using excimer laser or the like as a light source is a particularly urgent demand of the time, and a chemically amplified positive photoresist comprising an alkali-soluble resin, a dissolution inhibitor and a photo-induced acid precursor is viewed with interest. The function of this type of photoresist consists in transforming a dissolution inhibitor to a dissolution promotor by utilizing the acid generated upon exposure to light and baking, and thereby enhancing the dissolution velocity ratio between the unexposed area and exposed area of alkali-soluble soluble resin to improve the resolution. For example, the Extended Abstracts (the 38th Spring Meeting, 1991); the Japan Society of Applied Physics and Related Societies (29a-ZC-7) mentions the influence on the resolution of a chemically amplified positive photoresist composition comprising a resin prepared by partially replacing the --OH groups of polyvinylphenol with an acid removable protecting group, a dissolution inhibitor and a photo-induced acid precursor when the composition is exposed to a deep ultraviolet ray. In the paper, it is mentioned that the resin became insoluble in developing solution when the degree of replacement was elevated to 20% or above, that a ternary resist containing a dissolution inhibitor was higher than a binary resist containing no dissolution inhibitor in the dissolution velocity ratio at the time of development, and that a patterning evaluation of the ternary resist using an excimer laser stepper showed that a 0.35 .mu.m line-and-space could be resolved (FIG. 1).
In the Extended Abstracts (the 38th Spring Meeting, 1991); the Japan Society of Applied Physics and Related Societies (30a-ZA-3), it is mentioned that a chemically amplified positive photoresist composition comprising a novolac resin, a dissolution inhibitor having t-butoxycarbonyloxy group and a nonmetallic onium salt was applied to electron beam lithography. It is also mentioned that as the onium salt of this ternary system, triphenylsulfonium triflate was undesirable but bis(t-butylphenyl)-iodonium triflate (a) exhibited an excellent property. Further, it is also mentioned that the property of this resist system varied depending on the kind of the dissolution inhibitor having t-butoxycarbonyloxy group in such a manner that polymeric t-butoxycarbonyl compounds were not good in profile (overhanging patterns) though it exhibited an excellent dissolution inhibition. It is also mentioned that, among the dissolution inhibitors of this class, [t-C.sub.4 H.sub.9 OCO--O--C.sub.4 H.sub.4 ].sub.2.C(CH.sub.3).sub.2 (b) was best in sensitivity and resolution. It is also mentioned that tentative resists containing the above-mentioned (a) and (b), respectively, resolved a 0.15 .mu.m line-and-space pattern having a thickness of 0.47 .mu.m with an exposure dose of 14 .mu.C/cm.sup.2 in electron beam lithography (FIG. 1), and that the tentative resists were useful for X ray lithography, too, and could resolve 0.2 .mu.m contact holes in a thickness of 1.3 .mu.m.
In Claim 1 of EP-A-0388343, there is mentioned a resist for use in photon, electron beam and X ray exposure devices comprising (A) a polymeric or molecular composition, the solubility of which is dependent upon the presence of acid removable protecting groups and (B) a polymeric or molecular composition having a sulfonic acid precursor which generates a strong acid upon exposure to such radiation. In Example 5 of the specification, for example, a resist composition for use in a 240-260 nm exposing device comprising MDT (a kind of a photo-induced acid precursor), a novolac resin and [p-t-C.sub.4 H.sub.9 OCO--O--C.sub.6 H.sub.4).sub.2 ].C(CH.sub.3).sub.2 (dissolution inhibitor) is mentioned.
However, the photoresist compositions mentioned above are yet unsatisfactory in resolution, profile and sensitivity.